PLEASE MIND MY SPELLING MISTAKES.
Luffy: by mastering all three types of haki, luffy will discover gear 1, 4 and 5. Also with haki his strength and fighting style willl improve to Roger level.
Zoro: By having world's best swordman as his master his will enhance and become the second best swordman. I will sure that Mihawk will give zoro a leaving gift ( a awsome sword ). i guess Mihawk will drop zoro to the meeting place because Miwalk kows that if zoro goes alone he will get lost.
Sanji: of course Sanji will kick ass of all okama and will all 99 recips. he will also master the kama fighting techinques in the spare time and change the whole way of the island. I guess that robin will come to the kama kingdome with Ivancock and sanji and robin will go to the meeting place together (Sanji's dream come true).
Robin: By staying with the revolutniries robin will gain so much knowledge about the government, marins, new world and dragon. for robin, her knowlwdge is her power.
Franky: By knowing the advance technology of vegapunk, franky will build himself again and he will be the strongest cybote ( stronger then kuma). he wiil have incridable strength, beam ( luffy will admire franky for his whole life), strong body and he will also add so many cool weapones in Sunny Go making it the strongest ship.
Nami: by knowing the about new world's weather and how to create rain, tornado, lightning, snow and other weather, nami will be a weather witch( for sanji there will be something more to love her for).
Brook: brook will now play more instruments then just violanie. more instruments means more weapones.
Ussop: his current master will teach him about leathel weapons and will help him gain incrigable strengh.
he will descover three more transformation so that will make 10 in total. more knowlwdge about medicine and will learn how to hide properly.
OK I AM NOW SURE BUT THIS IS THE BEST I COULD THINK OF SO IF YOU AGREE OR DISAGREE "this is the best i could come up with.
thanks for reading and wasting your time